  (function (doc, win) {
        var docHTML = doc.documentElement,
        resizeEvtent = 'orientationchange' in window ? 'orientationchange' : 'resize',
        recalc = function () {
            var clientWidth = docHTML.clientWidth;
            if(clientWidth <= 720 && clientWidth > 0){
                docHTML.style.fontSize = 10 * (clientWidth / 720) + 'px';
            }else{
                docHTML.style.fontSize = 10 + 'px';
            }
        };
        if (!doc.addEventListener) return;
        win.addEventListener(resizeEvtent, recalc, false);
        doc.addEventListener('DOMContentLoaded', recalc, false);
    })(document, window); 